Comment on measuring photoionization cross sections of excited atomic states

The results of the measured absolute photoionization cross section from the 7² P excited states of cesium are reported. The following values have been obtained: (6.2±0.5)×10⁻¹⁸ cm² and (8.8±1.6)×10⁻¹⁸ cm² for the levels 7² P _1/2 and 7² P _3/2, respectively.     

Study of initiation reactivity of some plastic explosives by vacuum stability test and non-isothermal differential thermal analysis

On the basis of measurements of 18 high explosives by means of the Czech Vacuum Stability Test (VST) STABIL, a relationship has been specified between the results of this test and those of Russian manometric method. The said relationship was used to predict the Arrhenius parameters (E_a and log A values) of four plastic explosives based on RDX and one high explosive based on PETN (Semtex). The slopes E_aR⁻¹ of Kissinger's equation were specified by means of non-isothermal differential thermal analysis (DTA) and evaluation of the measurement results by means of the Kissinger method. The role played by binders and plasticizers in thermal decomposition of nitramines was pointed out on the basis of relationship between the E_a values obtained from VST and the E_aR⁻¹ values obtained from DTA, both for plastic explosives, eight nitramines, Composition B and PETN. The relationships between the E_aR⁻¹ values and thermostability threshold was specified for the given group of explosives. The relationship classify some of the studied plastic explosives as belonging to nitramines with steric hindrance in the molecule (CPX, TNAZ and HNIW). The relationship between E_aR⁻¹ values and drop energies, E_dr, sharply differentiates between plastic explosives and individual nitramines. From the relationship between the E_dr and D² values it was found that the increasing performance of the studied nitramines and plastic explosives is connected with the decrease in their impact sensitivity. Also specified are the approximate linear dependences between the peak temperatures of exothermic decomposition of all the explosives studied and their ignition temperatures, T_ig, or critical temperatures, T_c; these dependences were applied to prediction of T_ig and T_c of both the studied plastic explosives and some of the nitramines.     

Are pore size distributions in microfiltration membranes measurable by two-phase flow porosimetry?

The issue of evaluating equivalent pore diameter distributions in membrane microfilters from gas-liquid (g-l) porosimetry data has been critically examined. Experiments performed with one isotropic and one composite anisotropic membrane in both possible orientations revealed conspicous dependence of the obtained (g-l) porosimetry peaks on imposed pressure ramp rates, p. Interference of this kinetic effect can be eliminated from the measured data by extrapolation to p = 0. The ramp rate effect is most likely caused by tortuous pore length distribution, and relatively long times required for liquid expulsion. For two experiments, the observed effects of p could be reconciled with predictions of the Schlesinger-Bechhold theory [Bechold et al., Kolloid Z., 55 (1931) 172–198]. The data obtained with the thin top layer of the composite membrane facing intruding air directly did deviate somewhat from the theory. Pores characterized by (g-l) porosimetry are likely of the “throat type”, and their size distribution is considerably more narrow than that obtained for the “node-type” pores by SEM-image analysis [Zeman and Denault, J. Membrane Sci., 71 (1992) 221–231]. A single bivariate distribution function was constructed for these two distinct pore populations. Flow-weighted or number fraction distributions can be calculated from the extrapolated porosimetry data. For narrow ranges of “throat” diameters, these distributions are fairly similar.     

Extraction of Hg/II/ with dibutylester of N-/4-antipyryl/-amidophosphoric acid from iodide solutions

A new extraction reagent-dibutylester of N-/4-antipyryl/-amidophosphoric acid/DBAAP/—has been developed and used for the extraction of divalent mercury into chloroform from mixture of sodium iodide and perchloric acid. It was found that the composition of the species extracted into the organic phase depends on the acidity of the aqueous phase. The solvate HgI₂. DBAAP is extracted at low HClO₄ concentrations, an ion-pair, /DBAAPH/⁺.HgI ₃ ^– , is formed and extracted at high concentrations of perchloric acid.     

Possibilities of applying the Piloyan method of determination of decomposition activation energies

Activation energies (E) of the thermal decomposition and the initial valuesT _D of the exotherms are determined for trinitroaniline, trinitro-m-phenylenediamine, trinitrotriaminobenzene, trinitrophenol, trinitroresorcinol, trinitro-m-cresol and hexanitrooxanilide. Linear relationships are derived between the termsE.T _D ^1? and published kinetics data on these compounds, obtained by an isothermal manometric method. The mechanisms of the primary steps in the thermolyses of these polynitro compounds are discussed. A positive influence on their thermal stability has been confirmed, arising from the contact of the measured compounds with the glass surface.     

Possibilities of applying the Piloyan method of determination of decomposition activation energies in the differential thermal analysis of polynitroaromatic compounds and their derivatives

By means of non-isothermal DTA in its simple form the initial exotherm temperaturesT _D of 2,4-dinitrotoluene, 2,6-dinitrotoluene, 2,4,6-trinitrotoluene, 1,5-dinitronaphtalene, 1,8-dinitronaphthalene and 1,4,5,8-tetranitronaphthalene have been determined. By application of the Piloyan method to these measurements, the activation energiesE arising from the decompositions of these compounds were established. The results are discussed from the point of view of the molecular structures of the polynitro compounds.

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Zusammenfassung Durch nicht-isotherme DTA in ihrer einfachen Form wurde der BeginnT _D der Exothermen von 2,4-Dinitrotoluol, 2,6-Dinitrotoluol, 2,4,6-Trinitrotoluol, 1,5-Dinitronaphthalin, 1,8-Dinitronaphthalin, 1,4,5-Trinitronaphthalin und 1,4,5,8-Tetranaphthalin bestimmt. Durch Anwendung der Methode von Piloyan auf diese Messungen wurden die aus der Zersetzung o.a. Verbindungen herrührenden AktivierungsenergienE spezifiziert. Die erhaltenen Ergebnisse werden unter dem Aspekt der Molekularstruktur der untersuchten Polynitroverbindungen erörtert.

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Résumé On a déterminé par ATD les températures initialesT _D des phénomènes exothermiques du 2,4-dinitrotoluène, 2,6-dinitrotoluène, 2,4,6-trinitrotoluène, 1,5-dinitronaphtalène, 1,8-dinitronaphtalène, 1,4,5-trinitronaphtalène et 1,4,5,8-tétranitrophtalène. Les énergies d'activationE de la décomposition de ces composés ont été déterminées à l'aide de la mé thode de Piloyan. Les résultats obtenus sont discutés sous l'aspect de la structure moléculaire de ces composés.

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T _D 2,4-, 2,6-, 2,4,6- , 1,5- 1,8- , 1,4,5- 1,4,5,8- . , E .

     

Relationship between Electronic Charges at Nitrogen Atoms of Nitro Groups and Thermal Reactivity of Nitramines

Thermal reactivity of eleven nitramines has been examined by means of non-isothermal differential thermal analysis, and the data were analyzed according to the Kissinger method. The reactivity was expressed as the E _a R ⁻¹ slopes of the Kissinger relationship. Electronic charges, q ^N, at nitrogen atoms of the nitramine molecules were calculated by means of ab initio DFT B3LYP/6-31G** method. The relationships were confirmed between the slopes E _a R ⁻¹ and the q values for the nitro groups that are primarily split off. Conclusions are made in relation to the mechanism of initiation of polynitro compounds in general. This revised version was published online in July 2006 with corrections to the Cover Date.     

Possibilities of applying the Piloyan method of determination of decomposition activation energies in the differential thermal analysis of polynitroaromatic compounds and of their derivatives

Conditions are presented for application of the Piloyan method to the DTA of poly-nitro aromatic compounds. Activation energies (E) of the thermal decomposition and the initial valuesT _D of the exotherms are determined for trinitrotoluene, trinitro-m-xylene, trinitromesitylene, picryl chloride and dichlorotrinitrobenzene. Linear relationships are derived between the termsE · T _D ^? and published kinetic data on these compounds, obtained by an isothermal manometric method. The mechanisms of the primary steps in the thermolyses of these polynitro compounds are discussed. A negative influence on their thermal stability has been confirmed, arising from the contact of the measured compounds with the glass surface.